Described herein are solid compositions used in printed masks for printed circuit boards.
Printed circuit boards (PCBs) or printed wiring boards (PWBs) (hereinafter collectively PCBs) are platforms that connect and interface most electronic components with each other and with other elements in computers, communication devices, consumer electronics, automated manufacturing and inspection equipment. PCBs may be produced from a base of insulating material on which a thin copper layer is laminated or plated, known as a bare copper plated board, from which an etching step selectively removes areas of the copper to produce electrically conductive pathways.
This selective removal is achieved by applying a printed mask or photo-patterned etch-resist (photoresist) in a pattern on the copper layer. In the photo patterned case, the PCB is then subjected to a light source that causes the printed mask to become resistant a developer solution. The developer solution is then used to remove the unexposed photoresist leaving bare copper exposed in a pattern. In the printed mask case, the printed mask material is designed to be resistant to the acid etchant. In both cases, the PCB is then treated with an etchant such that areas of the copper plated board not coated with the patterned mask material are etched away, leaving just the pattern. The patterned mask material itself may then be removed with an aqueous base solvent, thereby leaving the electrically conductive pathways formed on the PCB.
Conductive layers on PCBs may also be produced by plating copper onto an insulating layer with a plating seed layer on the insulating layer. This process is often used as the outer layer process because it has the additional benefit of plating through holes in the PCB to allow layer interconnect. In the plating case, masking layers are described as in the etching case either by photoresist or printing, but instead of copper being treated with an etchant, the board is treated with a plating solution. The plating solution applies copper or other metals onto the surface of the board that is not covered by masking material. The masking material and the seed layer are then stripped off, leaving metal traces in the pattern.
In either process while the aqueous base solvent removes some of the printed mask, such removal is often inadequate or requires excessive processing time because these solvents do not strip off the printed mask quickly or in sufficient detail as to not require further removal effort, such as undercutting.